The present application relates to methods of manufacturing semiconductor devices, such as, for example, transistors, in III-V semiconductor substrates. Further aspects of the present application relate to surface passivation of semiconductor substrates and to sulfur-doping of III-V semiconductor substrates with nanoscale dimensional control.
Passivation of semiconductor materials during a manufacturing process may allow greater control over electrical properties of an integrated circuit generated by the manufacturing process. Passivation allows a manufacturer to protect surfaces of a semiconductor material or a semiconductor film stack to avoid the formation of oxides or to prevent the adhesion of contaminants to a semiconductor stack or material. Some passivation may protect semiconductor materials such as an intrinsic semiconductor (e.g., silicon) or compound semiconductors (e.g., III-V semiconductors such as, for example, GaAs) from reacting with atmospheric oxygen to form a native oxide layer on the top/exposed surface of the material. Native oxide layers may be removed from a semiconductor material with additional processing steps with concomitant increases in contaminants and/or defects. Undetected native oxide may modify an electrical characteristic of an integrated circuit, such as increasing contact resistance, reducing clock speed, or decreasing Ion for a transistor in an integrated circuit.
Semiconductor materials may be passivated by exposure of the semiconductor material to a sulfur source, wherein the sulfur interacts with the top/exposed surface of the semiconductor material to form a protective sulfur layer on the top/exposed surface of the semiconductor material. Sulfur deposition may be performed by applying a solution of ammonium sulfide (NH4)2S to the semiconductor material. However, use of ammonium sulfide has significant drawbacks. For example, at temperatures over 15° C., ammonium sulfide decomposes into ammonia and hydrogen sulfide, which are toxic to breathe or ingest. Manufacturing with ammonium sulfide uses costly exhaust systems to protect employees and facilities from exposure to toxic decomposition byproducts, and incurs higher waste disposal costs. Further, because ammonium sulfide solutions must be maintained at low temperatures to avoid decomposition into hydrogen sulfide, ammonium sulfide processing exhibits low rates of surface sulfurization (low rates of surface coverage, and thin sulfur film formation). Improvement to semiconductor passivation with sulfur (sulfurization) can improve protection against native oxide formation.
Doping of semiconductor materials to modify conductivity of a semiconductor material, or to modify a band gap of a semiconductor material, may be performed by implanting dopants into the semiconductor material. Implanting may involve accelerating a dopant atom to a high velocity and directing the accelerated dopant atom into a semiconductor material. An accelerated dopant atom may penetrate to a depth below the surface of the semiconductor material according to the mass of the dopant and the acceleration applied to the dopant atom before the dopant atom strikes the semiconductor surface. The penetration of the implanted dopant atoms may disrupt the crystal lattice of the semiconductor material, which disruption may be healed by an annealing operation performed after implanting of dopant atoms. Implantation into intrinsic semiconductor (e.g., silicon) and annealing of implanted intrinsic semiconductor may restore crystal structure to near-original condition. However, compound semiconductors such as III-V semiconductors may undergo irreparable damage following implanting and annealing. Localized stoichiometry may be disrupted after implant and annealing, resulting in small regions with deviations from the average stoichiometry of the bulk semiconductor material. Such deviations may result in lowered dopant activation, or higher junction leakage or leakage currents.
Sulfur may be used as a dopant for III-V semiconductors because sulfur atoms may be thermally diffused into III-V semiconductors without disrupting the crystal lattice, and without interrupting the uniform distribution of group III and group V atoms within the semiconductor material. Dimensions of a junction formed by thermal diffusion of sulfur may be regulated according to the annealing conditions used to thermally diffuse sulfur atoms into the semiconductor material. Sulfur-doping of III-V semiconductor substrates with nanoscale dimensional control may be improved with improvement in control and coverage amounts of sulfur on a semiconductor material.